Apparently I was mistaken about downgrade rights on OEM preinstallations and that OEM preinstallations do have downgrade rights:

Apparently, every Microsoft licensing rep has also lied to me for the past 10 years because my previous post was right out of their mouths. To downgrade OEM preinstalled operating systems I have always been forced to purchase SA "for downgrade rights" regardless of the size of business I was dealing with. Looks like I should be able to get a metric * ton of money back.

* Update: from URL above: Other OEM Windows 7 versions (for instance, Windows 7 Home Basic and Windows 7 Home Premium) do not include downgrade rights. Apparently, only Pro and Ultimate OEM installs get downgrade rights, not the home editions, which makes sense.